This invention relates to a method for partitioning a blood sample and obtaining clean serum from an unopened vacuum blood collection tube assembly.
Hospital clinical laboratories often analyse blood serum for various chemical constituents by using automated analyzers. Blood is drawn from a patient into a vacuum blood collection tube assembly. After the blood clots this tube is placed in a centrifuge which causes the clot material to move to the end of the tube distal to the stopper. The less dense serum is then between the clot material and the stopper.
Serum is then removed from the tube and presented by various methods to a blood serum chemistry analyzer. One method requires removal of the stopper and removal of serum by pipetting or decanting serum into a serum cup from which serum is dispensed to an analyzer. These operations may be automatic or manual or a mixture of these methods.
Serum may be removed from an unopened vacuum blood collection tube assembly following centrifugation without removal of the stopper by piercing the elastomeric stopper with a cannula so the distal end of the cannula is fully immersed in serum. Serum is then aspirated from the tube via the cannula by a syringe or pump and delivered to a serum cup or an analyzer. These operations may be manual or automatic or a mixture of these methods.
Various automated apparatus have been constructed to automate the operations of separating serum from the clot by centrifugation, removal of the stopper, and removing and dispensing of serum. Automation of centrifugal separation of serum and clot using conventional centrifuges has proven to be complex and costly due to the large number of separate operations required. These include the following:
(a) removing the blood tube from a carousel or rack
(b) placing the blood tube in a centrifuge rotor
(c) repeating (a) and (b) for a number of blood tubes
(d) balancing the centrifuge rotor
(e) closing the centrifuge lid
(f) rotating the centrifuge rotor for a predetermined time and speed sufficient to separate serum from the clot
(g) stopping the centrifuge rotor
(h) opening the centrifuge lid
(i) removing each tube from the centrifuge rotor
(j) placing each blood tube in a carousel or rack suitable for subsequent operations of serum removal and dispensing.
These operations have proven to be difficult to automate economically rendering this approach of limited value.
In an effort to more readily automate the centrifugation operation McEwen et al in U.S. Pat. No. 5,308,506 issued May 3, 1994 employ the method of rotating the vacuum blood collection tube assembly about its longitudinal axis. This method thus avoids most of the above (a) through (j) steps of conventional centrifugation. However, McEwen et al then employ a slidable piston positioned within the vacuum blood collection tube assembly during centrifugation to preserve the separation of serum and clot after rotation of the blood tube ceases. McEwen et al also use a special device shown on FIG. 8 of his patent to remove and dispense serum from an unopened vacuum blood collection tube assembly. Removal of serum from an unopened vacuum blood collection tube assembly is highly desireable since it avoids the generation of biohazardous aerosols sometimes generated by removal of the blood tube stopper, which have caused infection with HIV or hepatitis.
Mcwen et al invention suffers from the following shortcomings which have limited its utility:
1. It requires a special vacuum blood collection tube assembly containing a slidable piston which adds cost to the blood tube and adds to the laboratory stockroom more work and the need for more space.
2. It requires a special device to remove serum from an unopened vacuum blood collection tube assembly which adds cost to the process since the special device must either be disposable or must be washed after each use to avoid serum sample carryover problems.
3. It requires a special centrifuge apparatus to rotate the vacuum blood collection tube assembly about its longitudinal axis.
4. The operations of serum separation by centrifugation and removal followed by serum dispensing are all separate operations and are not integrated. They thus require manual interventions to move blood samples and serum samples from one apparatus to another and to dispense serum. These manual interventions lead to significant time and labor costs.
5. There is no provision for the removal from the dispensed serum contaminants such as air, microclots, cellular aggregations which can cause malfunction of automated serum chemistry analyzers.
Accordingly, in addition to avoiding many of the shortcomings and disadvantages of U.S. Pat. No. 5,308,506, further objects and advantages of the present invention are:
(a) to provide a single apparatus operating by a method which fully automates and integrates the operations of separation of serum from clots, removal of serum from an unopened vacuum blood collection tube assembly, and dispensing of removed serum to a remote receiver vessel.
(b) to provide the operations of (a) above while using a standard, unmodified vacuum blood collection tube assembly without any special features such as an enclosed slidable piston
(c) to provide the operations of (a) above without use of any one time use or disposable devices
(d) to provide the operations of (a) above and delivering clean serum free from contaminants such as air, microclots, cellular aggregates, or fibrin strands
(e) to provide clean serum from an unopened vacuum blood collection tube assembly including the operations of separating serum from the clot, removing and cleaning serum, and dispensing cleansed serum in a period of time of about 1 minute.
(f) to provide the operations of (e) above with significantly less cost for labor and materials than conventional methods
(g) to provide the operations of (e) above without use of devices requiring disposal
(h) to provide for the washing and drying of reusable serum conduits to reduce sample carryover effects to acceptably low levels
(i) to provide means for dispensing a predetermined volume of clean serum from an unopened vacuum blood collection tube assembly to a remote receiver vessel
Other objects and advantages will become apparent from a consideration of the ensuing description and drawings.